Astronaut Robert Curbeam is poised to set a new record next week when he is scheduled to embark on his fourth spacewalk of the space shuttle Discovery mission, this one to work on a stalled solar panel.

That would be the highest number of forays into space conducted by a crew member on a single mission.

Asked if she was concerned about fatigue, lead spacewalk officer Tricia Mack broke into a smile. "Really, if anyone can do it, it's Beamer," she said, using Curbeam's nickname. "He is rock solid."

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The fourth spacewalk was unplanned. NASA added it Saturday because several attempts have failed in completely retracting the solar panel.

Curbeam, a Baltimore native, came to the Discovery mission the most experienced crew member, both in terms of flight experience -- it would be his third trip to space -- and spacewalking experience, having done three prior spacewalks.

During the first spacewalk this mission, Curbeam helped install a 2-ton, $11-million addition to the international space station. He spent the second and third spacewalks rewiring the orbiting space lab from its interim power system to a permanent electricity grid.

NASA had to retract a solar array that was generating power for the temporary system to make way for new solar wings to begin rotating with the movement of the sun and produce power for the permanent system.

The old array retracted halfway on Wednesday before getting stuck, and since then, the space agency has tried a number of strategies in an attempt to fix it.

After completing their main tasks on Saturday's spacewalk, Curbeam and fellow spacewalker Sunita Williams headed over to the array to get a first-hand look at the problem. They found that a couple of grommets were stuck together and snagging the guidewire that runs through them.

The pair pushed on a box into which the accordion-like array folds, causing the 115-foot panel to shake. That managed to free some of the grommets and enabled other astronauts on the space station to retract the array further. But then more became stuck and the crew members' spacewalking time had run out.

So on Monday, Curbeam and Swedish astronaut Christer Fuglesang, who performed the first two spacewalks this mission, will go back out in an attempt to finish the job.

This time they will bring some tools along, each wrapped with insulated tape to protect against shock hazards. NASA managers hope the job can be completed within 6 1/2 hours, but said the spacewalkers will have as long as they need.

NASA decided to add the unplanned spacewalk because leaving it to later crews could delay scheduled objectives. The space agency is on a tight deadline to complete assembly of the space station by 2010, when the shuttle is due to retire.

The addition to the flight plan means Discovery will delay its landing by a day, from Thursday to Friday, after 13 days in space.

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